Comminuted crystalline phthalic anhydride



Patented Jan. 27,, 1931 UNITED STATES" PATENT" OFFICE LLOYD C. DANIELS,OF GRAFTON, AND CHRISTIAN J. SCHWIND'I, OF PITTSBURGH. PENNSYLVANIA,ASSIGNORS, BY MESNE ASSIGNMENTS, TO THE SELJDEN RESEARCH ENGINEERINGCORPORATION, OF PITTEBUBGH, PENNSYLVANIA, A QEBRPOBATION OF DELAWARECOHMINUTED CRYSTALLINE PHTHALIC .ANHYDRIDE No Drawing.

This invention relates to a phthalic anhydride product and to methods ofpreparing the same.

In the past phthalic anhydride from the catalytic oxidation ofnaphthalene has been obtainable in a number of forms. When purified bysublimation, the commercially most attractive process, phtha-l-icanhydride crystallizes into typical long needle crystals, butunfortunately, although possessing most desirable chemicalcharacteristics, the apparent density of the crystals is so low as togreatly increase the cost of containers and they will not pour from theordinary container such as a barrel. It has been proposed in the past toprepare phthalic anhydride in the form of flakes by meltin and passin itthrough any ordinary type oi flaking machine such as, for

example, a drum fia-ker. Flaked phthalic anhydride has a much higherdensity and can be readily poured from barrels, but has a number ofdisadvantages. in the first place the flaking operation, whichnecessitates a preliminary melting, makes easy the accidental inclusionof colored impurities as any colored impurity which is accidentallyincluded, even if only in a small portion of the material, isdistributed throughout the whole oi the melt and linked phthalicanhydride therefore frequently is not obtained in a pure white form. inthe second place, the fishing opera tion necessitates meltlng andprocessing with some loss in phthalic anhydride, which con siderablyincreases its cost. A further disadvantage of flaked phthalic anhydridelies in the tact that small amount of impurities which impart an odor tothe product are readily removed loy sublimation, but where flaking isused in connection with distillation'methods oi purification the producthe quently contains suilicient odor-lemming constituents to prohibit itsuse in the formation of certain esters where any odor is ohiectionable.It has also been roposed to pulverize or rind phthalic anhy ride ofvarious forms and the resulting powder, while it has a high apparentdensity, is an unsatisfactory prod- I not because of dusting, whichgreatly complicates packin and constitutes. a very serious,

fire danger, or phthalic anhydride dust, justi Application filed March22,

1930. Serial No. 438,235.

as the dust of any other organic compound, can form explosive mixtureswith air and tends to take on a high charge of static electricity.

The present invention is based on the'surprising discovery thatcrystalline phthalic anhydride can be comminuted or torn to a powder,without grinding, rapidlyand very cheaply and the process issubstantially free from dusting. The product resembles a flour which ismore or less coarse depending on the length of the comminution process.lt is of extraordinary whiteness and high apparent density. ,It can bepoured from a barrel with the same or greater case than flakes and itdissolves and melts even more rapidly than do the needle crystals.'lhese long needles are apparently disintegrated with utmost ease into acoarse our and any machine having disinte rating or tearing action canheemployed.

'0 easy is the comminution of the needles that even machines which areapparently utterly unsuitable, such as dough-mixing machines with rotarymixing arms can be used with great ei'lect. There is no, tendency of theneedle crystals to wrap around the arms and the operation is ofextraordinary rapidity. In small machines crystals can be transformedinto aliour in less than a minute and even in the largest machines thevoperation proceeds with great rapidity, As there is substantially noformation of fine dust the process does not present a the haaard andphthalic anhydride can be obtained in a dense, easily pourahle, fastmelting and dissolving form at a cost but a small fraction .of that offlaking and the. product is far superior to flaked phthalic anhydride,possessing all ofits advantages with none of its disadvantages, and atthe same time sharing the advantages of the long needle crystals fromwhich it is prepared.

minuted phthalic anhydride flour. The cost of, container is quite aconsiderable item, amounting to nearly a half-cent per pound in the caseof'needle crystals, as is also the saving in freight where, as is usual,the latter is charged primarily on the basis of volume rather thanweight.

The present invention can be carried out in any suitable disintegratorsuch as, for example, a dough-mixing machine or machines used in thecomminution. of cellulose fibers and can be carried out either as abatch process in machines which require batch operation or as acontinuous process in continuous feed disintegrators. The disintegrationwhen carried out as a batch process may be effected by incorporating alarge fraction of the batch at one time, but is preferably effected byfeeding the needle crystals in smaller portions as the power' requiredfor disintegration rises rapidly with high feed rates.

The invention can be practiced with any suitable disintegrator whichdoes not grind the product so as to produce dust, and the invention isnot limited to any particular type of disintegrator, the general typesmentioned above being merely illustrative examples of a few common typesin which the process can be carried out.

What is claimed as new is:

As a new product, comminuted crystalline phthalic anhydridesubstantially free from phthalic anhydride dust.

Signed at Pittsburgh, Pennsylvania, this 19th day of March, 1930.

- LLOYD C. DANIELS.

CHRISTIAN J. SCHWINDT.

